WASHINGTON (Reuters) - America's most sweeping expulsion of Russian diplomats since the Cold War may have seemed like a dramatic escalation in Washington's response to Moscow, but the groundwork for a more confrontational U.S. posture had been taking shape for months -- in plain sight.

While President Donald Trump's conciliatory rhetoric toward Moscow has dominated headlines, officials at the U.S. State Department, Pentagon and White House made a series of lower-profile decisions over the past year to counter Russia around the world - from Afghanistan to North Korea to Syria.

The State Department earlier in March announced plans to provide anti-tank missiles to Ukraine to defend against Russia-backed separatists in eastern Ukraine. Trump's predecessor as president, Barack Obama, had declined to do so over fears of provoking Moscow.

In Syria last month, the U.S. military killed or injured as many as 300 men working for a Kremlin-linked private military firm after they attacked U.S. and U.S.-backed forces. The White House, meanwhile, firmly tied Russia to deadly strikes on civilians in Syria's eastern Ghouta region.

Both the White House and Pentagon's top policy documents unveiled in January portrayed Russia as an adversary that had returned to the center of U.S. national security planning.

That was all before the United States said on Monday it would expel 60 Russian diplomats, joining governments across Europe in punishing the Kremlin for a nerve agent attack on a former Russian spy in Britain that they have blamed on Moscow.

Russia has denied any involvement.

With Monday's announcement, however, it was unclear whether Trump is promoting - or just acquiescing to - the tougher U.S. stance developed by his advisers and generals.

Trump's critics sought to portray him as a reluctant actor in any get-tough approach to Russia, even though one senior administration official described him as involved "from the beginning" in the expulsions of Russian diplomats.

"It is disturbing how grudgingly he came to this decision," said U.S. Representative Adam Smith, the top Democrat on the House Armed Services Committee.

Still, the Trump administration's actions run counter to widespread perception, fueled by the president's own statements, that Trump has softened America's stance toward Russian President Vladimir Putin amid a U.S. investigation into Moscow's meddling in the 2016 presidential election.

"U.S. signaling is all undercut by Trump's lack of seriousness about Russia," said Andrew Weiss, a Russia expert at the Carnegie Endowment for International Peace.

Just last Tuesday, Trump congratulated Putin on his re-election, drawing sharp criticism from fellow Republicans.

But in another sign of mixed messaging, Trump two days later named John Bolton, a strident Russia hawk, to become his national security adviser.

DOWNWARD SPIRAL

Although the nerve agent attack was the official trigger for the U.S. expulsions, Trump administration officials warned that the attack should not be viewed in isolation, citing a series of destabilizing and aggressive actions by Moscow.

In Afghanistan, Trump's top commander on the ground accused Russia again last week of arming Taliban militants.

On North Korea, Trump himself told Reuters in January that Russia was helping Pyongyang evade United Nations sanctions.

And less than two weeks ago, the Trump administration imposed the first sanctions against Russia for election meddling and cyber attacks, though it held off on punishing business magnates close to Putin.

U.S. officials and experts widely expect ties to further deteriorate, at least in the near term, and caution that Russia's next steps could extend far beyond retaliation against American diplomats.

"The risk of escalation doesn't just come from tit-for-tat punishments," said Matthew Rojansky, a Russia expert at the Wilson Center think tank in Washington, citing the potential for more aggressive moves from the Middle East to the cyber realm.

U.S. officials have said the Trump administration still seeks to avoid a complete rupture in bilateral relations. One official said Russian cooperation was still sought to address thorny diplomatic issues like North Korea and Iran.

(Additional reporting by John Walcott; editing by Mary Milliken and G Crosse)